Add app/bin/tools_copy_data.dart script
Add app/bin/tools_copy_data.dart script

This script can be used to populate a new project with data from an
existing project.

R=vegorov@google.com

Review-Url: https://codereview.chromium.org/2779223003 .

dart-lang/pub-dev,dart-lang/pub-dev,dart-lang/pub-dev,dart-lang/pub-dev